SU1742968A1 - Source of power supply for technological installations of direct current - Google Patents

Abstract

Use: The source can be used as a DC power source. SUMMARY OF THE INVENTION: The source contains a serial thyristor inverter consisting of two bridges 3, 4 and a filter 2 connected to the output of the rectifier input 1 via the input of the bridge, and the rectifier 8 through the transformer 5 to the load circuit. Each bridge includes two parallel-connected serial chains of inductive element 23 (24, 31, 32), valve cells 19

Description

The invention relates to electrical engineering, namely to semiconductor converters of alternating current electric energy with direct current with an intermediate link of increased frequency, and can be used as a source of direct current power in cases where a wide range of load current is combined with the requirement of small its pulsations with small dimensions and mass of passive filter circuits and the entire installation, for example, in electric arc technology, especially in arc welding, plasma and microplasma techno laser technology, adjustable DC drive, etc.

Power sources are known for direct current technological installations, comprising a series-connected and AC-powered transformer, a controlled rectifier and a filter, and a rectifier control system.

The disadvantage of such devices is the impossibility of obtaining low load currents (at high thyristor switching angles) for a given ripple and small dimensions of the filter and the entire installation. The disadvantage of this is due to the low (50 Hz) mains frequency, the constant and low ripple current. Taking into account that the dimensions and mass of the transformer of the installation increase with increasing load current, and the dimensions and mass of the filter decrease with decreasing current, as the range of the current expands towards small values, the equipment efficiency decreases due to deterioration of the weight and size parameters.

Other characteristics being equal, the best performance is provided by high-frequency AC power supplies, the structure of which includes an input rectifier connected in series and powered from an AC network, an input filter, an inverter, a transformer, an output rectifier filter and load circuit.

The control link in the power supply is an inverter, which can be made in the form of one or more bridge or half bridge circuits; In the inverter, various control methods can be used: pulse-width, phase, frequency-pulse. The latter method, in combination with a series resonant inverter, requires minimal elementary costs,

The device contains an input rectifier, an inverter, a transformer, an output rectifier, and an inverter control system containing a master oscillator, a load current sensor, comparison circuits, and a source of reference voltage, connected in series and powered from the AC mains.

The drawback of the device is the narrow control range of the process current, which is explained by the presence in the load circuit of a throttle (output filter), the effectiveness of which with the frequency-pulse control does not remain constant.

The closest in technical essence to the present invention is a device comprising an input rectifier connected in series, an input filter, a thyristor inverter, a transformer with primary and secondary windings, an output rectifier and a load circuit, and an inverter control system containing a master oscillator, a comparison circuit , the voltage source of the task, the pulse distributor, the current sensors and the load voltage, the current sensor being connected in series with the load circuit, its output is connected to the first input A comparison circuit, the second input of which is connected to the voltage source of the task through a divider.

The drawback of the device is the narrow range of the process current, which is explained by the following phenomena.

With frequency-pulse control (BAT), the power delivered by the inverter to the load is proportional to the ratio of the control frequency fy (the switching frequency of the inverter's thyristors) to the natural frequency of the inverter fo, determined by the parameters of the resonant switching circuit and the load resistance:

fn JI - T °

R

4 L where L is equivalent to the inductance of the switching circuit;

C - capacity of the switching capacitor:

R - contour resistance component is active.

To reduce the process current and, consequently, the power in the load, it is necessary to reduce fy. When fy becomes equal to 0.5 fo, the output current of the inverter becomes boundary-continuous, and with a further decrease in fy, it is discontinuous, having the form of alternating sinusoidal segments with a frequency fo, the duration of which is

1 / fo, and the repetition period is Ty 1 / fy 2 To. After a full-wave rectifier is rectified, the ripple frequency of the process current is fn 2 fy and decreases by decreasing the average value of the load current. Thus, in order, for example, to set the average value of the load current equal to half of the maximum limit current, it is necessary to choose fy 0.25 fo, while the rectified current will contain pauses with duration To.

Since a smoothed current is required to maintain the arc discharge and for many other purposes, a filter, in this case a smoothing inductance (choke), is included in the load circuit. It is known that the smoothing effect of a drossel is proportional to its inductance, current and frequency of pulsations; therefore, in the region of low current, when its frequency decreases, the efficiency of drossel decreases sharply. The choice of a high inductance calculated for the minimum current negatively affects the installation parameters in the high current region: losses grow, performance decreases, the mass of the output filter and the entire installation sharply increases due to the increase in the cross section of the throttle magnetic core. material and maximum load current. Thus, in the prototype, a wide range of load current is not provided with satisfactory weight and size indicators. The purpose of the invention is to expand the range of the process current in the direction of small values while maintaining the weight and size parameters.

The goal is achieved by the addition of three chains to the inverter, each of which is similar to the main one and contains the first inductive element connected in series, two pairs of anti-parallel connected thyristor and diode each, and the second inductive element connected in parallel to the main chain, with the output the other plate of the first capacitor is connected to the common point of connection of pairs from the anti-parallel connected thyristor and the diode of the first additional chain, the output of the other plate of the second st capacitor is connected to the common junction of the second additional pairs of similar chain, the total point compounds similar pairs of additional third chain is connected to the common junction of the pair of the main chain, and

the control system is additionally equipped with a second pulse distributor and a comparator, and the outputs of both pulse distributors through the OR circuit

connected to the control circuits of the thyristors of the chains, their inputs through the switch to the output of the master oscillator, the control input of the switch is connected to the output of the comparator, one input of which

0 is connected to the output of the current sensor and to another input of the comparison circuit, an output connected to the input of the master oscillator, and another input to the output of the reference voltage source.

5 In FIG. 1 shows the installation diagram; P-fig. 2 and 3 - external and adjusting characteristics; in fig. 4 is a variant of the circuit implementation of blocks 11-14.

Power supply for technological

0 units contain an AC power supply connected in series to an input rectifier 1 (Fig. 1), an input filter 2. a serial thyristor inverter consisting of two motors 3 and 4, a transformer 5 with a primary 6 and a secondary 7 windings and an output rectifier 8, a load circuit including a smoothing choke 9 and an active resistance 15, as well as an inverter control system containing a controlled master oscillator 10, a switch 11, two pulse distributors 12 and 13, an OR circuit 14, connected in series With load circuit 15, current sensor 16, comparator 17. comparison circuit 18 and reference voltage source (not shown in Fig. 1).

The inverters include: the first bridge - valve cells 19-22, which are anti-parallel thyristor and diode, inductive elements (inductors) 23-26, the second bridge - valve cells 27-30. coils 31-34. The output diagonals of the bridges are connected in parallel to the primary winding of the transformer by one poles directly, others through capacitors 35 and 36. The first input of the comparator 17 is connected to the output of current sensor 16 and to the first input of reference circuit 18, the second 0 to reference voltage source 37, output - to the control input of the two-position switch 11.

Depending on the state of the switch, the output of the master oscillator 10 is connected to the input of the first 12 or second 13 pulse distributors, the outputs of which through the OR circuit 14 are connected to the control circuits of the bridge thyristors 3 and 4. The output of the comparison circuit 18 is connected to the input of the master driver generator

10, and the voltage of the task is applied to the second input.

The power source works as follows.

When considering the operation of the device in dynamics, we will take the usual assumptions from the ideality of the valves and the transformer, the linearity of the passive elements of the inverter, the symmetry of the bridges.

Assume that switch 11 (FIG. 1) is in state 1; at the same time, the output pulses of the generator 10 are fed to the input of the first distributor 12, then through the OR circuit 14 to the control circuits of the thyristors.

The distributor 12 is constructed in such a way that it provides the following algorithm for controlling the thyristors of bridges 3 and 4: at the same time, the thyristors of the cells 19, 22, 27 and 30 are turned on; then the thyristors of the cells 20, 21, 28. 29 are simultaneously turned on; then again 19, 22, 27, 30 and so on. Suppose that this thyristor switching frequency fy and the load resistance correspond to the explanation 1 of the imaging point on the external characteristic 38 (Fig 2) and the position 1 on the adjustment characteristic (Fig. 3). When cells 19, 22, 27 30 are simultaneously turned on, the current of the rectifying filter 2 flows through two parallel branches, the first of which is formed by the series connection of coil 23, cell 19, capacitor 35, primary winding 6 of transformer 7, cell 22, coil 26. The second branch contains the coil 31, the cell 27, the capacitor 36, the winding 6, the cell 30, the coil 34, connected in series.

The impedance of the switching circuit, which is the main part of the output resistance of the inverter

, -f.

in this case, the inductance of the circuit L is equal to the inductance LK of one of the coils 23, 26, 31 or 34, and the capacity C is twice the capacitance Sk of one of the capacitors 35 or 36. Thus, in this case

p Vu / 2CK.

Assume that the process current decreases (this can be achieved by reducing the reference signal supplied to the

the second input of the comparison circuit 18 and, as a result, a decrease in the frequency fy. On the external and adjustment characteristics of the device (Figs. 2 and 3, respectively), this is represented by moving the operating point along the load line 39 from position 1, through position 2 in the direction of the arrow to point 3, which lies on the external characteristic 40 (Fig. 2).

0 Suppose that at point 3 the load current 15 (Fig. 2) reaches a threshold value n at which the magnitude of the signal from current sensor 16 is comparable to the reference voltage of source 37. Comparator 17 changes state (for example, from 0 to 1) which leads to a change in the state of the switch 11 from state 1 to state 2. The pulses of the generator 10 are now distributed by the second distributor 13, which is designed in such a way that the following algorithm is turned on for the thyristors of bridges 3 and 4: the thyristors of the cells 19 simultaneously turn on and 30, then I eat 21 and 28, then 27 and 22. then 20 and 29, again

5 19 and 30 and so on.

When cells are simultaneously turned on, for example, 19 and 30. The current of the rectifying filter 2 flows through one branch formed by successive

0 connecting the coil 23, the cells 19, the capacitor 35, the winding 6, the cells 30, the coil 34. In this case, the inductance of the circuit L is equal to twice the inductance LK of one of the coils, the capacitance C 5 of capacitance Sk of one capacitor 35 or 36. and the characteristic impedance pi Y2 LK / CK 2 pi. those. 2 times increased.

In order to maintain the selected current value of 1P with an increased output resistance of the inverter, the comparison circuit 18 produces a signal leading to an increase in the frequency fy and an abrupt movement of the imaging point from position 3 on the adjustment characteristic 41 (Fig.

5 3} to position 3 on the adjustment characteristic 42.

On the external characteristics (Fig. 2), the position of point 3 is retained, but the characteristics themselves change the configuration (paragraph 3) in the drawing, correspond to the inverter with new parameters, namely, their steepness increases, the same load power is reached large value fy. With a further decrease in load current na5, the points depicted in FIG. 2 and 3 move in direction 4. (As the load current increases, the frequency fy increases, the image point moves from position 4 to position 3, and if the current exceeds n, comparator 17 (Fig. 1) returns to O, the switch goes to 1, and the inclusion in the structure of the first pulse distributor 12 reduces the output impedance of the inverter, which is necessary to obtain large values of the load current.The further path of the imaging point on the external characteristic: 3-2-1, on the adjusting one, in jumps 3-3-2-1 So, if For reasons of smoothing current pulsations or for other reasons, the minimum allowable value of the inversion frequency is minimized, then, as can be seen from FIG. 3, the change in the switching algorithm of inverter bridge valves described above allows limiting the minimum load current to lo instead of In, characteristic of prototype. The expansion of the range of the technological current in the direction of smaller values is AI 1P - lo (Fig. 3), which in practical cases corresponds to 20-30%. Since the frequency of inversion does not fall below the value of mines, the mass and dimensions of the throttles 9 in the load circuit 15 (Fig. 1) and the installations as a whole are preserved,

The increase in the number of elements included in the inverter bridges by 4 times as compared with the prototype does not significantly affect the weight and dimensions of the installation for the following reasons. With the same installation power in the proposed device, the valve cell and inductance coil current is 4 times less than in the prototype, which is explained by the presence of two bridges and the use of the total voltage of the rectifying filter 2 (FIG. 1) instead of 0.5 of this value in the prototype, namely, the magnitude of the current determines the mass and dimensions of these elements. In addition, their dispersion improves thermal conditions, increases the efficiency of the cooling system.

All other things being equal, the total capacitance of capacitors 35. 36 is the same as in the prototype. The additional positive effect of the invention is manifested when operating on an arc load, since in the low current mode (welding of metals of small thickness, the standby mode of the plasma torch, the stage of refining in an arc furnace, etc.), the resistance of the power source increases, the external characteristic approaches vertical, which leads to an increase in the stability of the discharge, the stabilization of its current, and a decrease in the probability of an arc break.

Implementing blocks 11-14.

The output of the controlled generator 10 is connected to the counting input of the T-flip-flop 43, to

the second input circuit And 44 and to the first input circuit And 45. The output of the trigger 43 is connected to the first input circuit And 46, the second input of which is connected to the output of the circuit NOT 47, and the output to the second input circuit And 46 and to the second inputs of the circuit 48 -55. The input of the circuit NOT 47 is connected to the second input of the circuit I 45, to the second inputs of the circuit I 56-63 and to the output of the comparator 17. The outputs of the circuits I / I 45, 46 are black;

the circuit OR 64 and the circuit of the first input-output circuit AND 44 are connected to the input of the annogow counter 65 with a conversion factor 4, the outputs of which are connected to the first inputs of the circuits AND 48-63, and their outputs through the circuits

OR 66-73 and the formation and galvanic isolation circuits - with the control electrodes of the thyristors of valve cells 19-22, 27-30, in pairs form the following connections: 66-19, 67-20, 68-21, 69-22, 70 -27, 71-28,

72-29, 73-30. In this embodiment, the role of the switch 11 is performed by the NOT 47 circuit in combination with logic elements 48-63, the IL 14 circuit is implemented on the elements 66–73. Common elements are used in the distributors for 12 and 13 pulses to reduce hardware costs.

If the output of the comparator 17 receives a signal O, the pulses of the generator 10, the frequency of which is divided into two by the trigger 43, through

elements 46, 64, 44 are fed to the input of the ring counter 65. From its outputs, through elements 48-55, forming a controllable decoder, and the OR circuit 66-73, these pulses flow into the control circuits of the thyristors of the inverter bridges 3, 4, and the switching sequence thyristor provides low output impedance of the inverter.

When the comparator 17 changes its state from 0 to 1 when the current decreases, the generator 1.0 pulses go to the input of counter 65. trigger 43 turns on. The controllable decoder changes its structure so that

its elements 56-63, from the outputs of which through the elements 66-73, the pulses enter the control circuits of the thyristors of the inverter bridges 3 and 4, and the turn-on sequence of the thyristors

provides high output impedance of the inverter. In both cases, the switching frequency of the thyristors is two times lower than the frequency of the pulses of the generator 10.

In this way, switching of distributors 12 and 13 pulses by means of switch 11 according to the output logic signal of comparator 17 can be realized. This is represented in the form of a functional diagram in FIG. one.

i i174296812

It follows from the foregoing that the supplied pairs of thyristors and diodes are designed to expand the range to process the output of the inverter connected to the current in the direction of small values by the transformer's primary winding, while retaining the weight and dimensions of the secondary winding of which is connected The vyley is achieved by introducing a new elec- trover rectifier, to the output of which subsets and connections, namely: an autonomous switched load circuit, and also the inverter system is made in the form of two bridges, inverter control containing the tasks of which, through the capacitors, the connecting generator, the comparison circuit, are supplied to the primary winding of the transformer, the voltage of the reference, the distributor, and the second pulse, the current sensor, the switch, the pulse limiter circuit, are introduced into the control system, the switch and the OR circuit, the reference voltage source, in- OR, the outputs of the first and second distribution current sensors are connected in series with the telephones via the OR circuit connected to the control circuit of the load, one input of the circuit compares the inverter thyristors ora, is connected to the source of the voltage set by the inputs through the switch - to the output of the task, characterized in that, for the purpose of a generator, the control input of the commutation of the range of the technology controller to the output of the comparator current in the direction of its small values with a co-offered power source for the storage of mass and size parameters, logical settings of direct current gives an additional possibility of changing its parameters parallel to the inverter input, in 20 but the second chain is introduced from third connected inductive part without commutation of high-current element, two pairs of counter-parallel circuits, and has stable and stable paired thyristor and diode, each and four meters with arc load, full inductive element, those. educated due to a substantial (2 times) 25 van symmetrical bridge, parallel to the entrance of the internal resistance growth of the source-inverter, a second similar power supply and a corresponding increase in the bridge are included, other plates of the external characteristics of the external slots are related to common connection points pairs of small currents, where the arc discharge of the thyristors and diodes is additionally introduced is subject to external influences. 30 sequential chains, common point. The formula of the invention of the thyristor pair connection and diodes

The power supply for technological other chains of both bridges are combined; a second distributed-connected input pulse separator and a comparator, directing outputs, an input filter, a series 35 of the first and second distributors are inserted into the direct-current installations. a thyristor inverter, including ow, through the OR circuit, is connected to the control — two capacitors, outputs of one of the plates of the inverter thyristors, the inputs of which are combined into a common point, and the circuit through the switch p - to the output of the master current from the series-connected primary controller, the control input of the switch inductive element, two pairs of 40 to the output of the comparator, one input of which is connected to the current sensor output and to the primary and a diode each, and a second inductive mu input of the comparison circuit, another one to the source, with free leads for the reference voltage, the second input of the ductive elements form the input of the comparison circuit and the common connection point 45 the voltage of the task and its output are to the input of the condensers and the common connection point of the generating generator.

Fig.Z

46

43

T

G w

TG1 I

Lf

w l

uu

40

U

From the vines. / 3 wci.

S6

ffS

to SO

/

59

41

, 1Q

li -

72 K29

73 R30

Claims (1)

Claim A power source for technological DC installations containing a series-connected input rectifier, an input filter, a series thyristor inverter, including two capacitors, the outputs of one of the plates of which are combined into a common point, and a chain of series-connected first inductive elements, two pairs of counter-parallel connected thyristor and diode each, and the second inductive element, and the free terminals of the inductive elements form the inverter input, and the common connection point capacitors and a common point of connection of these pairs of thyristors and diodes form the inverter output connected to the primary winding of the transformer, to the secondary winding of which an output rectifier is connected, to the output of which a load circuit is connected, as well as an inverter control system containing a master oscillator, a comparison circuit, a source reference voltage, pulse distributor, current sensor, switch, OR circuit, reference voltage source, the current sensor being connected in series with the load circuit, one circuit input Comparison is connected to the reference voltage source, characterized in that, in order to expand the range of the technological current to the side of its small values while maintaining weight and size indicators, a second chain of three inductively connected third in series elements is additionally introduced parallel to the inverter input, two pairs of counter-parallel connected thyristor and diode each and the fourth inductive element, i.e. a symmetrical bridge is formed, a second similar bridge is connected parallel to the inverter input, other capacitor plates are connected to common points of connection of pairs of thyristors and diodes of additionally introduced sequential chains, common points of connection of pairs of thyristors and diodes of other chains of both bridges are combined, a second pulse distributor is introduced into the control system and a comparator, the outputs of the first and second pulse distributors through the OR circuit are connected to the control circuits of the inverter thyristors, the inputs through the switch p - to the output of the master oscillator, the control input of the switch to the output of the comparator, one input of which is connected to the output of the current sensor and to the first input of the comparison circuit, the other to the source of the reference voltage, the second input of the comparison circuit is connected to the source of the reference voltage, and its output is to the input of the master oscillator. 4-3 FIG. 3 t6 ~ FIG. At